A brace of goals from on-loan striker Mickael Antoine-Curier sealed Brentford's Division Two safety to plunge toothless Chesterfield further into the mire.
Antoine-Curier stuck twice either side of half time to condemn the Spireites to a fifth straight league defeat, and only results from elsewhere prevented the Derbyshire club from sliding into the relegation zone.
And worse news was to hit Chesterfield as they finished the game with nine men after strikers Kaleb Folan and Chris Brandon were both stretchered off with serious injuries which are likely to rule them out for the remaining games of the campaign.
But it was the home side who settled marginally the better in this relegation six- pointer with Brandon wasting a good opportunity on 21 minutes when he fired wastefully wide with team-mate Glynn Hurst well positioned for a cross at the back post.
But, against the run of play, Brentford took the lead when Stephen Hunt crossed from the left and Antoine-Curier volleyed home at the far post.
Anyone hoping for a second half revival was soon to be disappointed when the striker, on loan from Nottingham Forest, doubled the lead on 55 minutes when a Mark Peters corner was headed across the goal by Kevin O'Conner and Antoine-Curier prodded the ball over the line from barely a yard.
Ten minutes later he should have completed his hat-trick when a cross from Peters found him unmarked six yards from goal, but he wastefully sent his header over the bar.
Mark Hudson drew a suberb save from Paul Smith with a 20-yard effort but it was to prove the home team's only shot on goal in the entire match.
And, though David Reeves wasted his team's best chance with a header over the bar in the last seconds of an incredible 10 minutes of stoppage time, it was Brentford who could have added further to the tally.
Firstly Muggleton reacted well to smother Peters' surge into the penalty area and then Matt Somner grazed a header high and wide from substitute Jay Tabb's free-kick.
Chesterfield's fans were crying for manager Dave Rushbury to be sacked at the final whistle as they now seem resigned to a nail biting last two games of the season.